There are two traditional secondary side rectification schemes for a flyback switching power supply circuit, wherein one is asynchronous rectifier scheme, i.e., using a diode (as shown in FIG. 1A), and the other one is synchronous rectifier scheme (as shown in FIG. 1B). The synchronous rectifier scheme is to control a rectifier SR2 to be turned on and off by a gate driving signal. FIG. 2 illustrates characteristics of the power consumption of a diode and a rectifier. In practical applications, a working range of a low-power flyback switching power supply circuit is in the shadow region shown in FIG. 2. In the shadow region, a power consumption characteristic curve 12 of the rectifier is below a power consumption characteristic curve 11 of the diode, i.e., the power consumption of the rectifier is lower than the power consumption of the diode. Therefore, the synchronous rectifier scheme can realize less power consumption than the asynchronous rectifier scheme, thus obtaining higher conversion efficiency. Low power consumption generates less heat, so the temperature characteristic of the rectifier is also superior.
The secondary side rectification scheme is widely applied to notebook power adapters, wireless communication devices, LCD power management, and Ethernet power supplies because of its high conversion efficiency. With the development of electronic technology, it is necessary to propose a secondary side rectification scheme with both high efficiency and good robustness.